1. Field of the Invention
The invention relates to storage devices and, particularly, to magnetic recording media used in storage devices such as hard disks for computers, and a method for the production thereof.
2. Description of the Related Art
A magnetic recording medium used in a hard disk or the like is made up of a non-magnetic substrate and thin films of magnetic materials formed on the substrate. Performance of a thin magnetic layer is prone to be effected by the material of an underlying layer. It is thus common to provide an underlayer between a magnetic layer and a non-magnetic substrate in order to improve performance of the magnetic layer.
At present, a magnetic recording medium in which an underlayer of chromium (Cr), nickel (Ni), or an alloy based on them is formed on a non-magnetic substrate, and on which a film of alloy based on cobalt (Co), such as a Co--Cr--Ta alloy, Co--Cr--Pt alloy or the like, is formed, is used as a medium allowing a high storage density. Hard disks for computers are required to have large storage capacity, and to this end, it is required that magnetic recording media have a much higher storage density. Thus, magnetic recording media is required to have a higher coercivity and a reduced media noise.
On the other hand, magnetic recording media represented by hard disks are requested to have smoothness and resistance to shock due to a recent trend towards a small head flying height. Accordingly, glass substrates which are superior in those properties to the aluminum substrates predominantly used at present are attracted attention. Examples of magnetic recording media using a glass substrate are given in Japanese Unexamined Patent Publications No. 6-96431, No. 5-325163, etc., all of which use Cr or an alloy thereof for an underlayer under a magnetic layer. They also describe interposing an intermediate layer of Cu, Ti, Al or the like between the Cr layer and the glass substrate in order to improve the magnetic properties and the recording and read back properties. For example, Japanese Unexamined Patent Publication No. 6-96431 discloses a magnetic recording medium in which an intermediate layer of Cu or the like is interposed, so as to prevent oxygen and the like, from a substrate, from reaching a Cr underlayer and make (110) face of Cr parallel to the surface of a substrate, to thereby improve the magnetic and magnetic recording properties.
Japanese Unexamined Patent Publication (Kokai) No. 8-171716 discloses a magnetic recording medium in which an underlayer consisting of a compound of Ni and P is directly formed on a non-magnetic substrate. However, a magnetic recording medium in which a Ni-based non-magnetic compound is used for an underlayer, and an intermediate layer is interposed between a glass substrate and the underlayer, is not known.